This invention relates to an automatic container filling apparatus of the type that continuously fills moving containers with a liquid or other fluent material, and particularly to such container filling apparatus which uses a single supply of regulated air at a predetermined pressure above atmospheric in controlling the flow of product to a container. More particularly, this invention relates to an automatic container filling apparatus which includes a sensor tube arranged to be positioned in a container to be filled where high pressure air flows out of the tube during filling and when the product reaches the sensor tube the back pressure realized causes the container filling operation to cease.
There are various known automatic container filling machines wherein a sensing tube extends into a container to be filled and when the lower end of the tube is blocked by the product in the container back pressure through the tube actuates a control device to stop the flow of product to the container. The known filling machines generally use two sources of air pressure as elements of the control functions for the filling operation. High pressure air is directed through the control system to open the product fill valve and to blow out the sensor tube of residual product prior to filling. Low pressure air is directed to the sensor tube and to auxiliary control elements such as pneumatic compensator devices. The compensators function to sense the high pressure control air and any back pressure derived from the sensor tube when the product level in the container being filled reaches the sensor tube. The differential pressure between the high pressure control air and the back pressure will result in the fill valve of this system closing the flow of product to the container. The compensators are generally complicated devices often using resilient diaphragms across chambers containing the high pressure control air and back pressure air from the sensor tube. The diaphragms also define a chamber between them containing atmospheric air which enters and exits the chamber through a vent port. The interaction between the diaphragms and the throttling of atmospheric air from the intermediate chamber function to control the product fill valve. The diaphragms will stretch in response to the pressurized air acting on them in order to stabilize into their control orientations. The venting of atmospheric air also has a bearing on the functioning of the diaphragms.
The automatic container filling machines using dual air pressure control and pressure compensating systems have inherent drawbacks. Aside from requiring expensive separate high and low air pressure sources, the complex and sensitive compensators are subject to errors resulting from diaphragms stretching and developing leaks over prolonged periods of use. When either the stretching or leaking occurs false signals are sent from the compensator to the controller and the filling operation may be terminated too late, resulting in overfilling the container. The venting of compensators also causes problems. It is common for venting in a low pressure atmosphere to be irregular, resulting in inconsistent pressure response being communicated to the controller. Such inconsistent pressure responses may cause unequal container filling. Venting of air is also costly since the air used in filling systems is most often treated air or in some instances nitrogen, both of which are expensive items.
The dual air pressure filling systems also require sensitive components for diverting high pressure air from one component to another as well as to the compensators for venting. Shuttle valves are common for diverting the high pressure air. The low pressure air also calls for components within the low pressure air circuitry. The higher the number of components required in the system, the higher the expense of the system as well as the greater the need for maintenance and replacement. Whenever component parts are replaced in the system, time comsuming and necessarily expensive recalibration of the system using expensive special instrumentation is required.
This invention overcomes the inherent drawbacks of the heretofore known automatic filling machines of the type described by providing a machine using a single regulated high pressure air supply for controlling the flow of product to the container to be filled. The use of a single source of control air in my system eliminates the need of a pressure balancing compensator, or the like, as well as the need for venting of control air and control pressure diverting components. My automatic filling machine uses a significantly lower number of component parts as compared to the heretofore known systems, resulting in a system which is relatively inexpensive as compared to the known systems as well as a system which is simple in its operation and has low maintenance requirements. In addition, the components of my system are relatively simple in construction and their replacement is easy and not nearly as expensive as replacement of the complicated compensators and other component parts of the known systems. Also, my system does not require any expensive, time consuming recalibration whenever any of the component parts are replaced. My system is also simply packaged and installation on new or existing filling machines is easily achieved by two connections, namely to the fill sensor tube and product source. Thus, my invention provides an inexpensive, automatic container filling apparatus which uses a single source of regulated air to control the filling operation without changing the air pressure while using a significantly low number of relatively simple and insensitive component parts, eliminating the need for system recalibration whenever component parts are replaced. The single source of regulated air results in simple, direct pressure control as compared with complex differential pressure control of the known systems.